1. Field of the Invention
This invention relates to an electrodynamic loudspeaker, for low and medium sound frequencies, having a movable diaphragm, an oscillatory coil connected to this diaphragm and, in the area of an air gap a magnetic assembly. The magnetic assembly includes permanent magnets which can be traversed by an alternating current which represents an electric signal to be converted into audible sound.
2. Prior Art
In known loudspeakers of this kind the diaphragm is either of funnel, dome or calotte shape. When set into oscillation it transmits sound in a selected direction. From this it follows that for good stereophonic or quadrophonic sound reproduction known loud speakers have to be arranged in such a way that the sound waves emitted therefrom converge at one point or one area in which the listeners should be located. This leads to drawbacks and limitations, firstly regarding the positioning of the loudspeaker and secondly in relation to the number of listeners who can be located in the preferred listening area. In addition, known loudspeakers have to be installed in cabinets, for example of closed box form or bass reflex cabinets, and in some cases must have carefully calculated acoustic screening or dampening to avoid any acoustic short circuiting with sound waves radiated from the rear side of the diaphragm. These known loudspeakers arranged in boxes or cabinets are therefore frequently bulky and due to the additional cost of the cabinet, relatively expensive.
It is recognised that the total acoustic output of a loudspeaker is proportional to the radiating outer face, the square of the amplitude of movement of the diaphragm and the square of the frequency. Otherwise stated, in a loudspeaker of the known kind, the diaphragms act substantially as a piston, the radiating face of which is proportional to the square of the diameter of the circle defined by the outer edge of the diaphragm. As a consequence in the case of low sound frequencies, and for a prescribed diameter of diaphragm, the amplitude of the movement of the diaphragm must be large to achieve a high acoustic sound output.